Gas turbine engines of modern aircraft require a supply of oil to mechanical components such as, but not limited to, bearings, seals, and the like. The oil can be used as a lubricant, a coolant, or both for these components. Typical oil systems supply the oil to a manifold which then directs the oil to different engine components. In some systems, the oil then progresses to a tank for holding the oil before it is pumped back to the components to lubricate them again. In other systems, the oil is simply pumped back to the engine components and stored in a sump at each component. When the oil leaves the tank it is filtered to remove unwanted debris and de-aerated to remove any air absorbed by the oil while lubricating and cooling the components. An oil cooler also removes additional heat gained from the lubricated components. Commonly, the fuel for the engine is used as the coolant, as the fuel moves quickly in relation to the oil allowing the fuel to absorb a large amount of heat from the oil. Other lubrication systems may have the filter, de-aerator, or cooler arranged in the system such that the oil interacts with these components after leaving the engine components but before returning to the tank or sump.
In prior art oil systems, the quantity of oil pumped to the components is typically based on a high speed and high load condition, or is regulated based on the speed of the engine. However, either approach often results in an oversupply of oil, at least in low load conditions, such as during cruise or a high altitude climb, for example. This reduces the efficiency of the engine in that the excess oil is churned by the engine component, imparting extra heat to the lubricant. This lubricant then needs to be cooled before being used as a coolant or lubricant for the engine components again and thereby drawing power from the engine. Additionally, the bulky coolers needed for cooling the oil increase the weight of the engine, and in turn weight of the aircraft, thereby reducing fuel economy. In light of the foregoing, it can be seen that an oil system is needed that can provide oil in the quantity needed under the specific load and speed conditions the engine is experiencing.